diff --git a/test/speed/array1.cpp b/test/speed/array1.cpp
index 57225345..263ad379 100644
--- a/test/speed/array1.cpp
+++ b/test/speed/array1.cpp
@@ -137,8 +137,8 @@ struct foreach_manual_simple {
   const int u[2] = {1,0}; //=1, u1=0;
   //int u[2]; for (int i=0; i<2; ++i) u[i] = 1-i;
   for (int k =0; k<5000; ++k)
-   for (t[u[0]]=0; t[u[0]]<A.len(u[0]); ++t[u[0]])
-    for (t[u[1]] =0; t[u[1]]<A.len(u[1]); ++t[u[1]])
+   for (t[u[0]]=0; t[u[0]]<A.shape(u[0]); ++t[u[0]])
+    for (t[u[1]] =0; t[u[1]]<A.shape(u[1]); ++t[u[1]])
      A(t[u[1]],t[u[0]]) = 1876;
   //A[t] = 1876;
  }
diff --git a/test/speed/array_short1.cpp b/test/speed/array_short1.cpp
index 474795c5..640c7a23 100644
--- a/test/speed/array_short1.cpp
+++ b/test/speed/array_short1.cpp
@@ -137,8 +137,8 @@ struct foreach_manual_simple {
   const int u[2] = {1,0}; //=1, u1=0;
   //int u[2]; for (int i=0; i<2; ++i) u[i] = 1-i;
   for (int k =0; k<5000; ++k)
-   for (t[u[0]]=0; t[u[0]]<A.len(u[0]); ++t[u[0]])
-    for (t[u[1]] =0; t[u[1]]<A.len(u[1]); ++t[u[1]])
+   for (t[u[0]]=0; t[u[0]]<A.shape(u[0]); ++t[u[0]])
+    for (t[u[1]] =0; t[u[1]]<A.shape(u[1]); ++t[u[1]])
      A(t[u[1]],t[u[0]]) = 1876;
   //A[t] = 1876;
  }
diff --git a/test/triqs/arrays/dot.cpp b/test/triqs/arrays/dot.cpp
index 58eb14dc..19d5f95e 100644
--- a/test/triqs/arrays/dot.cpp
+++ b/test/triqs/arrays/dot.cpp
@@ -52,7 +52,7 @@ int main(int argc, char **argv) {
 
  test<vector<double> , vector<int> >();
  
- // does not work for array just because of .size() vs .len(0)...
+ // does not work for array just because of .size() vs .shape(0)...
  //test<array<double,1> , array<int,1> >();
  //test<array<double,1> , vector<int> >();
  //test<vector<double> , array<int,1>  >();
diff --git a/triqs/arrays/blas_lapack/stev.hpp b/triqs/arrays/blas_lapack/stev.hpp
index 62bf9fd1..1b62eb63 100644
--- a/triqs/arrays/blas_lapack/stev.hpp
+++ b/triqs/arrays/blas_lapack/stev.hpp
@@ -49,7 +49,7 @@ namespace triqs { namespace arrays { namespace blas {
     D(range(0,s)) = d; 
     E(range(0,s-1)) = e;
     int info;
-    f77::stev ('V',d.size(),D.data_start(),E.data_start(), Z.data_start(), Z.len(0),W.data_start(), info);
+    f77::stev ('V',d.size(),D.data_start(),E.data_start(), Z.data_start(), Z.shape(0),W.data_start(), info);
     if (info !=0) TRIQS_RUNTIME_ERROR << " Error in tridiagonal matrix diagonalization "<< info;
    }
   arrays::vector_view<double> values() const { return D(range(0,s));}
diff --git a/triqs/arrays/impl/indexmap_storage_pair.hpp b/triqs/arrays/impl/indexmap_storage_pair.hpp
index 57516bab..37ef7422 100644
--- a/triqs/arrays/impl/indexmap_storage_pair.hpp
+++ b/triqs/arrays/impl/indexmap_storage_pair.hpp
@@ -166,8 +166,6 @@ namespace triqs { namespace arrays {
 
     size_t shape(size_t i) const { return domain().lengths()[i];}
 
-    size_t len(size_t i) const { return this->shape()[i]; }
-
     size_t num_elements() const { return domain().number_of_elements();}
 
     //bool is_empty() const { return this->num_elements()==0;}
diff --git a/triqs/arrays/matrix_stack_view.hpp b/triqs/arrays/matrix_stack_view.hpp
index b21e7c36..d5c0242f 100644
--- a/triqs/arrays/matrix_stack_view.hpp
+++ b/triqs/arrays/matrix_stack_view.hpp
@@ -44,9 +44,9 @@ namespace triqs { namespace arrays {
  
    matrix_view<T> view(size_t i) const { return a(i,range(),range());}
    
-   size_t size() const { return a.len(0);}
-   size_t dim0() const { return a.len(1);}
-   size_t dim1() const { return a.len(2);}
+   size_t size() const { return a.shape(0);}
+   size_t dim0() const { return a.shape(1);}
+   size_t dim1() const { return a.shape(2);}
 
    matrix_stack_view & operator +=(matrix_stack_view const & arg) { a += arg.a; return *this; }
    matrix_stack_view & operator -=(matrix_stack_view const & arg) { a -= arg.a; return *this; }
diff --git a/triqs/arrays/matrix_view_proxy.hpp b/triqs/arrays/matrix_view_proxy.hpp
index 777388a3..11f25d10 100644
--- a/triqs/arrays/matrix_view_proxy.hpp
+++ b/triqs/arrays/matrix_view_proxy.hpp
@@ -34,7 +34,7 @@ namespace triqs { namespace arrays {
  // to do : separate the array and the matrix case.
  // generalize with preprocessor (draft below)
 
- // write concept mutable down and clean it (dim0, dim1, len(i), ...) 
+ // write concept mutable down and clean it (dim0, dim1, shape(i), ...) 
 #ifdef DO_NOT_DEFINE_ME
  // human version of the class, the preprocessor generalisation is next..
  template<typename ArrayType > class const_matrix_view_proxy<ArrayType,2> : TRIQS_MODEL_CONCEPT(ImmutableMatrix)   {
@@ -47,9 +47,9 @@ namespace triqs { namespace arrays {
    typedef typename indexmap_type::domain_type domain_type;
    indexmap_type indexmap() const { return slicer_t::invoke(A->indexmap() , range() , range(),n, ellipsis()); }
    domain_type domain() const { return indexmap().domain();}
-   size_t len(int i) const { return A->len(i);}
-   size_t dim0() const { return A->len(0);}
-   size_t dim1() const { return A->len(1);}
+   size_t shape(int i) const { return A->shape(i);}
+   size_t dim0() const { return A->shape(0);}
+   size_t dim1() const { return A->shape(1);}
    typename ArrayType::storage_type const & storage() const { return A->storage();}
    TRIQS_DELETE_COMPOUND_OPERATORS(const_matrix_view_proxy);
    template< typename A0 , typename A1 , typename ... Args> value_type const & operator() ( A0 &&a0 , A1 &&a1 , Args && ... args) const
@@ -66,9 +66,9 @@ namespace triqs { namespace arrays {
    typedef typename indexmap_type::domain_type domain_type;
    indexmap_type indexmap() const { return slicer_t::invoke(A->indexmap() , range() , range(),n, ellipsis()); }
    domain_type domain() const { return indexmap().domain();}
-   size_t len(int i) const { return A->len(i);}
-   size_t dim0() const { return A->len(0);}
-   size_t dim1() const { return A->len(1);}
+   size_t shape(int i) const { return A->shape(i);}
+   size_t dim0() const { return A->shape(0);}
+   size_t dim1() const { return A->shape(1);}
    typename ArrayType::storage_type const & storage() const { return A->storage();}
    template<typename RHS> matrix_view_proxy & operator=(const RHS & X) {triqs_arrays_assign_delegation(*this,X); return *this; }
    TRIQS_DEFINE_COMPOUND_OPERATORS(matrix_view_proxy);
@@ -92,9 +92,9 @@ namespace triqs { namespace arrays {
    typedef typename indexmap_type::domain_type domain_type;\
    indexmap_type indexmap() const { return slicer_t::invoke(A->indexmap() BOOST_PP_ENUM_TRAILING(POS, TEXT, range()),n, ellipsis()); }\
    domain_type domain() const { return indexmap().domain();}\
-   size_t len(int i) const { return A->len(i);}\
-   size_t dim0() const { return A->len((POS+1)%3);}\
-   size_t dim1() const { return A->len((POS+2)%3);}\
+   size_t shape(int i) const { return A->shape(i);}\
+   size_t dim0() const { return A->shape((POS+1)%3);}\
+   size_t dim1() const { return A->shape((POS+2)%3);}\
    typename ArrayType::storage_type const & storage() const { return A->storage();}\
    value_type const * restrict data_start() const { return &storage()[indexmap().start_shift()];}\
    value_type * restrict data_start() { return &storage()[indexmap().start_shift()];}\
@@ -117,9 +117,9 @@ namespace triqs { namespace arrays {
    typedef typename indexmap_type::domain_type domain_type;\
   indexmap_type indexmap() const { return slicer_t::invoke(A->indexmap() BOOST_PP_ENUM_TRAILING(POS, TEXT, range()),n, ellipsis()); }\
    domain_type domain() const { return indexmap().domain();}\
-   size_t len(int i) const { return A->len(i);}\
-   size_t dim0() const { return A->len((POS+1)%3);}\
-   size_t dim1() const { return A->len((POS+2)%3);}\
+   size_t shape(int i) const { return A->shape(i);}\
+   size_t dim0() const { return A->shape((POS+1)%3);}\
+   size_t dim1() const { return A->shape((POS+2)%3);}\
    typename ArrayType::storage_type const & storage() const { return A->storage();}\
    value_type const * restrict data_start() const { return &storage()[indexmap().start_shift()];}\
    value_type * restrict data_start() { return &storage()[indexmap().start_shift()];}\
diff --git a/triqs/lattice/bravais_lattice_and_brillouin_zone.cpp b/triqs/lattice/bravais_lattice_and_brillouin_zone.cpp
index 101e6238..f93df772 100644
--- a/triqs/lattice/bravais_lattice_and_brillouin_zone.cpp
+++ b/triqs/lattice/bravais_lattice_and_brillouin_zone.cpp
@@ -29,7 +29,7 @@ namespace triqs { namespace lattice_tools {
  //using triqs::arrays::blas::dot;
  const double almost_zero(1E-10);
 
- bravais_lattice::bravais_lattice( units_type const & units__) : units_(3,3), dim_(units__.len(0)) { 
+ bravais_lattice::bravais_lattice( units_type const & units__) : units_(3,3), dim_(units__.shape(0)) { 
   units_(range(0,dim_),range()) = units__();
   units_(range(dim_,3),range()) = 0;
   // First complete the basis. Add some tests for safety
diff --git a/triqs/lattice/tight_binding.cpp b/triqs/lattice/tight_binding.cpp
index 34723b0d..4d357aa8 100644
--- a/triqs/lattice/tight_binding.cpp
+++ b/triqs/lattice/tight_binding.cpp
@@ -31,8 +31,8 @@ using namespace std;
 
  array_view <dcomplex,3> hopping_stack (tight_binding const & TB, array_view<double,2> const & k_stack) {
   auto TK = Fourier(TB);  
-  array<dcomplex,3> res(TB.n_bands(), TB.n_bands(), k_stack.len(1));
-  for(size_t i = 0; i<k_stack.len(1); ++i) res(range(), range(), i) = TK(k_stack(range(),i));
+  array<dcomplex,3> res(TB.n_bands(), TB.n_bands(), k_stack.shape(1));
+  for(size_t i = 0; i<k_stack.shape(1); ++i) res(range(), range(), i) = TK(k_stack(range(),i));
   return res;
  }
 
@@ -131,14 +131,14 @@ using namespace std;
 
   //const size_t ndim=TB.lattice().dim();
   //const size_t norb=TB.lattice().n_orbitals();
-  int ntri = triangles.len(0)/3;
+  int ntri = triangles.shape(0)/3;
   array<double,1> dos(neps);
 
   // Check consistency
   const size_t ndim=TB.lattice().dim();
   //const size_t norb=TB.lattice().n_orbitals();
   if (ndim !=2)  TRIQS_RUNTIME_ERROR<<"dos_patch : dimension 2 only !";
-  if (triangles.len(1) != ndim) TRIQS_RUNTIME_ERROR<<"dos_patch : the second dimension of the 'triangle' array in not "<<ndim;
+  if (triangles.shape(1) != ndim) TRIQS_RUNTIME_ERROR<<"dos_patch : the second dimension of the 'triangle' array in not "<<ndim;
 
   // Every triangle has ndiv*ndiv k points
   size_t nk = ntri*ndiv*ndiv;
diff --git a/triqs/lattice/tight_binding.hpp b/triqs/lattice/tight_binding.hpp
index a9b0d60c..9dfd349f 100644
--- a/triqs/lattice/tight_binding.hpp
+++ b/triqs/lattice/tight_binding.hpp
@@ -55,8 +55,8 @@ namespace triqs { namespace lattice_tools {
      std::vector<long> V(std::forward<VectorIntType>(v)); 
      if (v.size() != bl_.dim()) TRIQS_RUNTIME_ERROR<<"tight_binding : displacement of incorrect size : got "<< v.size() << "instead of "<< bl_.dim();
      matrix<dcomplex> M(std::forward<MatrixDComplexType>(m));
-     if (M.len(0) != n_bands()) TRIQS_RUNTIME_ERROR<<"tight_binding : the first dim matrix is of size "<<  M.len(0) <<" instead of "<< n_bands();
-     if (M.len(1) != n_bands()) TRIQS_RUNTIME_ERROR<<"tight_binding : the first dim matrix is of size "<<  M.len(1) <<" instead of "<< n_bands();
+     if (M.shape(0) != n_bands()) TRIQS_RUNTIME_ERROR<<"tight_binding : the first dim matrix is of size "<<  M.shape(0) <<" instead of "<< n_bands();
+     if (M.shape(1) != n_bands()) TRIQS_RUNTIME_ERROR<<"tight_binding : the first dim matrix is of size "<<  M.shape(1) <<" instead of "<< n_bands();
      displ_value_stack.push_back(std::make_pair(std::move(V), std::move(M)));
     }